Find the missing number in the fraction pattern

1 / 2 = 2 / 4 = 3 / ? = 4 / 8
What number should replace the question mark?

1 / 3 = 2 / 6 = 3 / 9 = 4 / 12 = 5 / ? = 6 / 18
What number should replace the question mark?

2 / 3 = 4 / 6 = 6 / ? = 8 / 12
What number should replace the question mark?

3 / 8 = 6 / 16 = 9 / ? = 12 / 32
What number should replace the question mark?

1/ 5 = 2/ 10 = 3 / 15 = 4 / ? = 5 / 25
What number should replace the question mark?

2 / 7 = 4 / 14 = 6 / 21 = 8 / ? = 10/35
What number should replace the question mark?

10 / 12 = 15 / 18 = 20 / 24 = 25 / ?
What number should replace the question mark?

21 / 28 = ? / 24 = 15 / 20 = 12/16
What number should replace the question mark?

14 / 35 = 12 / 30 = 10 / ? = 8 / 20 = 6 / 15
What number should replace the question mark?

6 / 7 = 12 / 14 = 18 / 21 = 24 / ? = 30 / 35
What number should replace the question mark?